Numerical Investigation of Geometry Effects on Flow, Heat Transfer and Defrosting Characteristics of a Simplified Automobile Windshield with a Single Row of Impinging Jets

The effect of jet geometry on flow, heat transfer and defrosting characteristics was numerically investigated for elliptic and rectangular impinging jets on an automobile windshield. Initially, various turbulence models within the commercial computational fluid dynamics (CFD) package FLUENT were employed and validated for a single jet, and the results indicated that the impinging jet heat transfer was more accurately predicted by the SST k -ω turbulence model, which was then utilized for this study. The aspect ratios (AR) of elliptic and rectangular jets were respectively 0.5, 1.0, and 2.0, with jet-to-target spacing h/d=2, 4 and jet-to-jet spacing c/d=4, and all those situations were numerically analyzed with the same air mass flow and jet open area. It was observed that the heat transfer coefficient and defrosting performance of the inclined windshield were significantly affected by the shape of the jet, and the best results were obtained with the elliptic jet arrangements. The average Nusselt number (Nu) of the entire windshield exhibited a considerable increase with the AR changing from 1 to 2 for both the elliptic and rectangular jets, whereas it varied a little with the AR changing from 0.5 to 1. Compared with the jets with lower AR, a substantial improvements (roughly 40% increase) in defrosting area could be achieved by utilizing the elliptic jet with AR=2 due to higher turbulence level and wider velocity spreading. Additionally, the results quantitatively demonstrated that the defrosting performance of the windshield not only depended on the average Nu, but more importantly on the uniformity of the air flow impinging on the whole windshield.